US6813307B1 - Module channel for acquiring and tracking in a radio communication system - Google Patents

Module channel for acquiring and tracking in a radio communication system Download PDF

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Publication number
US6813307B1
US6813307B1 US09/581,043 US58104300A US6813307B1 US 6813307 B1 US6813307 B1 US 6813307B1 US 58104300 A US58104300 A US 58104300A US 6813307 B1 US6813307 B1 US 6813307B1
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channel
system information
synchronization
logical channel
telecommunications system
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Michel Cohen
Emmanuel Lemois
Laurent Cuvelier
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RPX Corp
Nokia USA Inc
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Alcatel SA
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/19—Earth-synchronous stations
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7073—Synchronisation aspects
    • H04B1/7075—Synchronisation aspects with code phase acquisition
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0602—Systems characterised by the synchronising information used
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B2001/70706—Spread spectrum techniques using direct sequence modulation using a code tracking loop, e.g. a delay locked loop
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/709—Correlator structure
    • H04B1/7093—Matched filter type
    • H04B2001/70935—Matched filter type using a bank of matched fileters, e.g. Fast Hadamard Transform

Definitions

  • the present invention relates to the field of communications by radio. More particularly, it relates to time and frequency acquisition and tracking in radiocommunications systems. It applies in particular to cellular radiocommunications systems, to cellular radiocommunications systems using satellites, or to other wireless radiocommunications systems.
  • a user station which generally does not have accurate clock generator means, must acquire time and frequency synchronization with a transmitter station in order to be able to demodulate the signals it receives from said transmitter station. It is also essential for a user station to be able to perform tracking in time and in frequency, i.e. to maintain time and frequency synchronization throughout a call so as to enable it to continue correctly demodulating the signals it receives.
  • Physical channels are defined in such radiocommunications systems enabling information to be transmitted and typically corresponding to a carrier frequency; such physical channels are subdivided into logical channels, e.g. by time division or by code division, so as to provide multiple access on a single physical channel.
  • Time division multiple access (TDMA) and code division multiple access (CDMA) are known per se.
  • Communicating with user stations in a radiocommunications system also requires system information to be broadcast to the stations by using a logical channel associated with a physical channel.
  • the system information can comprise the name or the number of the base station (“gateway”), or the geographical location in cell terms.
  • the term “broadcast” is used below to designate transmitting such system information, and the term “traffic” is used to designate the content of the messages interchanged with users.
  • the data rate for system information is usually quite low compared with the data rate for traffic, and is typically a few kilobits per second.
  • constraints in such a radiocommunications system lies in reaching all of the user stations in the coverage zone, including those which are least favored from the propagation point of view. This constraint is in addition to constraints associated with limitations on spectrum and power resources specific to each type of system.
  • the invention proposes a solution to the problem of acquiring and tracking synchronization in a radiocommunications system. It also proposes a solution to the problem of broadcasting information to user stations.
  • the invention proposes using a single logical channel, preferably without increasing power, both for the purposes of acquiring and tracking synchronization in time and frequency, and also for broadcasting system information.
  • the invention provides a synchronization channel for a radiocommunications system between a plurality of stations, the system having a detection word that is repeated on the channel, and system information that occurs between repetitions of the detection word.
  • the repetitions of the detection word form a periodic pattern in the channel, the period of the pattern being a submultiple or a multiple of a frame period of the channel.
  • the detection word can also be repeated periodically, at a period that is a submultiple or a multiple of a frame period of the channel.
  • the system information is transmitted on the channel after being spread.
  • the spreading is spreading by M-ary modulation using a Hadamard code.
  • the system information is encoded by an error correcting code.
  • the invention also provides a radiocommunications system having such a synchronization channel.
  • the system has a plurality of physical channels, each physical channel having at least one logical channel; the synchronization channel is a logical channel.
  • the logical channels are defined by code division multiple access.
  • FIG. 1 is a diagram showing the appearance of a synchronization channel of the invention
  • FIG. 2 is a diagram of a transmitter for such a channel
  • FIG. 3 is a diagram of a receiver for such a channel
  • FIG. 4 is a graph showing bit error rate as a function of signal-to-noise ratio for different frequency differences.
  • FIG. 5 is a graph of bit error rate as a function of signal-to-noise ratio for different types of error correcting code.
  • Each code defines a logical channel which can be used for traffic or for broadcasting system information; it is possible to define a frame which may itself be subdivided into elementary time slots; the size of the code or of the time slots, and the corresponding data rates depend on the characteristics of each system and can vary.
  • the invention proposes using a single logical channel, preferably without increasing power, and to do so for all of the functions associated with acquiring and tracking synchronization and with broadcasting system information.
  • the corresponding channel is referred to as the “synchronization” channel.
  • the synchronization channel corresponds to a logical channel, i.e. all or part of a carrier or of a physical channel.
  • FIG. 1 shows the appearance of the synchronization channel.
  • a synchronization word 1 is repeated on the synchronization channel at a given periodicity.
  • the synchronization channel carries system information 2 for broadcasting to the user stations.
  • the size, the structure, and the power of the detection word depend on the characteristics of the system in question, and they are selected so as to enable user stations to acquire synchronization, and where appropriate to track synchronization.
  • the detection word also referred to in practice as the “unique” word, presents a high degree of self-correlation and a low probability of appearing in a transmitted message. These properties make it easier to detect the detection word on the channel.
  • Repetition of the detection word in the synchronization channel enables a user station to acquire time synchronization by recognizing the detected word in the logical channel.
  • recognition of the detected word enables the user station to acquire symbol synchronization.
  • the detection word is thus preferably repeated at a period that corresponds to the frame period.
  • repetition of the detected word can be periodic or otherwise.
  • repeats of the detection word advantageously form a periodic pattern in the channel, where the period of the pattern is a submultiple or a multiple of the frame period of the channel.
  • the detection word can also be repeated once only per frame.
  • the detection word is repeated periodically at a period which is a submultiple or a multiple of the frame period.
  • a user station can thus acquire symbol and frame synchronization merely by recognizing the detection word.
  • a first frequency estimate can be made by conventional techniques, e.g. by the developed phase method.
  • the invention proposes broadcasting system information. It is thus possible on a single logical channel to transmit all of the elements required for user station synchronization.
  • the invention thus makes it possible to avoid using up system resources, and it reduces the impact of the acquisition and synchronization functions on the transmission capacity of the system.
  • the solution of the invention also makes it possible to vary the effective data rate with which system information is broadcast without any spectrum modifications.
  • system information is transmitted over the logical channel after spreading, and each symbol of the logic channel conveys not an entire symbol of system information, but a portion of a symbol, known as a “chip”, that results from the symbols of the system information being spread.
  • the broadcast data rate in terms of number of system information symbols broadcast per second, or the real information data rate, is then lower; nevertheless, system information spreading remains possible while using only one logical channel, in particular because of the low data rate required for system information.
  • This embodiment makes it possible to increase the signal-to-noise ratio of system information symbols for a given level of signal-to-noise in the logical channel. This ensures that even those user stations which are the least favored from the propagation point of view receive system information correctly; as a result the invention provides a high degree of robustness.
  • System information symbol spreading can be performed by conventional spreading techniques, e.g. as described by M. K. Simon et al., in “Spread spectrum communications” published by Computer-Science Press, 1988.
  • the description below with reference to FIG. 2 shows an implementation for Hadamard codes as a specific example of M-ary modulation.
  • the use of Hadamard codes for spreading system information prior to being broadcast on the synchronization channel between the detection words is particularly advantageous because demodulation is non-coherent; this increases its ability to withstand variations of phase and frequency.
  • FIG. 2 is a diagram of a transmitter for a synchronization channel of the invention.
  • the example shown in the figure uses Hadamard M-ary modulation for spreading system information symbols, and quaternary phase shift keying (QPSK) for modulating the carrier.
  • QPSK quaternary phase shift keying
  • the system information symbols to be transmitted are initially grouped together in groups of n, as shown at 4 .
  • each group of n symbols is then associated with a line of the Hadamard matrix, i.e. 2 n symbols or Hadamard symbols, at the data rate of the carrier.
  • the corresponding M-ary modulation constitutes spreading of the system information symbols to be transmitted.
  • the Hadamard symbols obtained after spreading are transmitted to a multiplexer 6 .
  • the multiplexer also receives the detection word symbols, see reference 7 in the figure.
  • the multiplexer 6 multiplexes the Hadamard symbols and the detection word symbols to obtain a symbol structure of the kind shown in FIG. 1 .
  • the system information symbols at the nominal data rate of the carrier, and multiplexed with the detection word symbols, are then modulated on the logical channel.
  • the specific processing can vary.
  • the symbols modulated on the carrier are sampled, and then multiplied by the sequence or code corresponding to the channel, prior to being applied to the physical channel.
  • system information is transmitted on the logical channel at a data rate D.n/2 n . That is the instantaneous data rate, and no account is taken of the space occupied in the carrier by the detection word.
  • the power of the detection words in the channel can be different from the power of the transmitted system information. This applies in particular for the case when the system information is transmitted after a first stage of spreading, as in the embodiment described; under such circumstances, the first stage of spreading serves to increase the signal-to-noise ratio of the system information. That means it can be transmitted at a lower level while still being received by user stations under the least favorable reception conditions.
  • FIG. 3 is a diagram of a receiver for a synchronization channel of the invention, capable of operating with the transmitter of FIG. 2 .
  • the symbols received over theological channel where appropriate after synchronization has been acquired on the chips when using CDMA logical channels, are applied to a block 10 for acquiring time synchronization and symbol synchronization; in the block 10 , the receiver looks for the detection word and also, where appropriate, proceeds with frame synchronization. It is possible at this instant to proceed with a first estimate of frequency, as explained above.
  • the symbols are then demultiplexed at 11 so as to separate transmitted system information from detection words.
  • the system information received between the detection words at the nominal data rate of the channel is then grouped together in groups of 2 n symbols, in block 12 .
  • a fast Hadamard transform is applied to the groups of 2 n symbols at 13 .
  • the line of the transmitted Hadamard matrix is then determined at 14 so as to enable the n transmitted information symbols to be obtained; with this being performed typically by using the criterion of maximum likelihood concerning the line of the Hadamard matrix.
  • the information symbols are determined at 15 .
  • the invention makes it possible to estimate frequency difference and phase difference.
  • This estimation makes it possible firstly to track the physical channel so that the user station continues to be latched on the transmission frequency of the physical channel.
  • this estimation makes it possible to correct the frequency and the phase of signals received on other logical channels on the same physical channel; as a result the invention makes it possible, on a single channel, to group together the functions of estimated both frequency difference and phase difference on a physical channel.
  • Tracking the detection words also makes it possible to maintain time and symbol synchronization in the user station.
  • FIG. 4 is a graph showing bit error rate (BER) as a function of signal-to-noise ratio for different frequency differences; the signal-to-noise ratio E s /N 0 is plotted in dB along the abscissa and the bit error rate of the system information is plotted up the ordinate.
  • the curve plotted with lozenges shows simulated results without any frequency difference; the curve plotted with squares shows simulated results for a frequency difference lying in the range ⁇ 400 Hz to +400 Hz, with equiprobable distribution between those two values.
  • the curve plotted with triangles shows simulated results for a frequency difference of 400 Hz.
  • phase and frequency difference are advantageously determined not from the Hadamard lines, but from the system information symbols as corrected by applying the error correcting code.
  • the corrected system information symbols serve to recover the transmitted Hadamard line, and the transmitted line (or plurality of lines) is compared with the symbols actually received on the carrier.
  • FIG. 5 is a graph of the bit error rate on the system information or of the symbol error rate (SER) as obtained after spreading, as a function of the signal-to-noise ratio for different types of error correcting code.
  • the notation is the same as in FIG. 4 .
  • the curve plotted with black lozenges shows the symbol error rate, and the curve plotted with black triangles shows the bit error rate, without an error correcting code.
  • the two curves plotted using squares show the symbol error rate and the bit error rate when using a Reed Solomon (70, 84) type error correcting code.
  • the two curves plotted using triangles show the symbol error rate and the bit error rate when using a Reed Solomon (56, 84) type error correcting code.
  • the figure shows that using error correcting codes considerably improves the performance of the transmission system.
  • the probability of a frequency error greater than 21 Hz is about 10 ⁇ 6 for system information bit modulation using 128 symbols.
  • a Reed Solomon (8, 12) type error correcting code a shortened code which corrects two errors, probability of about 10 ⁇ 8 is obtained.
  • system information symbol spreading is obtained by using Hadamard codes; this is not essential for implementing the invention, and it would also be possible to use other types of spreading code.
  • the invention has also been described in the context of logical channels that are defined by orthogonal CDMA type codes; it applies equally well to other types of multiple access, using time division multiple access (TDMA) or frequency division multiple access (FDMA), or indeed logical channels defined in other ways.
  • TDMA time division multiple access
  • FDMA frequency division multiple access
  • the entire synchronization channel is used for acquiring and tracking synchronization, and for broadcasting information; these functions could be achieved using only a portion of the synchronization channel. Under such circumstances, the remainder of the synchronization channel could be used for traffic.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Astronomy & Astrophysics (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • General Physics & Mathematics (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)
  • Detection And Prevention Of Errors In Transmission (AREA)
US09/581,043 1998-10-26 1999-10-25 Module channel for acquiring and tracking in a radio communication system Expired - Lifetime US6813307B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FR9813374A FR2785118B1 (fr) 1998-10-26 1998-10-26 Canal module d'acquisition et de poursuite pour un systeme de radiocommunications
FR9813374 1998-10-26
PCT/FR1999/002583 WO2000025450A1 (fr) 1998-10-26 1999-10-25 Canal module d'acquisition et de poursuite pour un systeme de radiocommunications

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US (1) US6813307B1 (fr)
EP (1) EP0998065A1 (fr)
JP (1) JP2002529002A (fr)
KR (1) KR20010033604A (fr)
CN (1) CN1287724A (fr)
AU (1) AU6345499A (fr)
BR (1) BR9907061A (fr)
FR (1) FR2785118B1 (fr)
TW (1) TW432814B (fr)
WO (1) WO2000025450A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080137617A1 (en) * 2005-02-15 2008-06-12 Jurgen Michel Code Sequence and Radio Station
RU2510933C2 (ru) * 2012-06-22 2014-04-10 Открытое акционерное общество "Российский институт мощного радиостроения" Устройство синхронизации в системе радиосвязи с программной перестройкой рабочей частоты
US20200305220A1 (en) * 2016-03-31 2020-09-24 Nec Corporation Radio access network node, radio terminal, network node, and method therefor

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3677185B2 (ja) * 1999-11-29 2005-07-27 株式会社東芝 符号分割多重伝送方式と送信装置及び受信装置
US8023398B2 (en) 2007-01-30 2011-09-20 Qualcomm Incorporated Using a single FHT to decode access-based handoff probes from multiple users
CN111614373B (zh) * 2020-05-20 2021-08-10 北京升哲科技有限公司 扩频信号发送、扩频信号接收方法、装置、设备及介质

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080137617A1 (en) * 2005-02-15 2008-06-12 Jurgen Michel Code Sequence and Radio Station
US8542664B2 (en) * 2005-02-15 2013-09-24 Siemens Aktiengesellschaft Code sequence and radio station
RU2510933C2 (ru) * 2012-06-22 2014-04-10 Открытое акционерное общество "Российский институт мощного радиостроения" Устройство синхронизации в системе радиосвязи с программной перестройкой рабочей частоты
US20200305220A1 (en) * 2016-03-31 2020-09-24 Nec Corporation Radio access network node, radio terminal, network node, and method therefor

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BR9907061A (pt) 2000-10-17
CN1287724A (zh) 2001-03-14
FR2785118B1 (fr) 2004-06-18
WO2000025450A1 (fr) 2000-05-04
TW432814B (en) 2001-05-01
JP2002529002A (ja) 2002-09-03
EP0998065A1 (fr) 2000-05-03
FR2785118A1 (fr) 2000-04-28
KR20010033604A (ko) 2001-04-25
AU6345499A (en) 2000-05-15

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